The present invention relates to a novel electron beam-curable resist composition and a method for fine patterning using the same. More particularly, the invention relates to an electron beam-curable resist composition having excellent storage stability and capable of being developed with a developer solution containing an organic alkali compound without the trouble due to scum formation to give a patterned resist layer having an ideally orthogonal cross sectional profile of a line pattern with a high contrast of the images so as to be useful in the manufacturing process of various kinds of semiconductor devices such as transistors, ICs, LSIs, VLSIs and the like as well as to a method for forming a very finely patterned resist layer on a substrate surface by using the resist composition.
Semiconductor devices, such as transistors, ICs, LSIs, VLSIs and the like, are manufactured in a process usually involving a step of photolithography, in which a substrate, such as a semiconductor silicon wafer, is provided on the surface with a coating layer of a photosensitive resin composition and the photosensitive layer is exposed patternwise to light through a photomask bearing the image of a pattern followed by a development treatment and rinse treatment to form a patterned photoresist layer and an etching treatment or a dopant-diffusion treatment on the areas uncoated with the resist layer by repeating the above described procedure several times according to need so as to form an electronic circuit on the substrate surface.
It would be a due expectation in view of the trend in the semiconductor industry in recent years toward increasing fineness in the works of semiconductor processing that the density of integration in semiconductor memories will be upgraded to 16 MDRAMs, 64 MDRAMs, 256 MDRAMs, 1GDRAMs and even higher in the near future. This trend in the electronic industry requires finer and finer working in the photolithographic process of semiconductor processing giving rise to many proposals and attempts relative to improvements in the resist materials and exposure appratuses by minifying projection of light.
For example, it is an already established technology that a resist pattern having a line width of as fine as 0.4 to 0.5 .mu.m can be obtained by the combined use of a positive-working photoresist composition comprising a specific novolac resin and a naphthoquinone diazide compound and a minifying projection exposure apparatus of high precision. It is, however, accepted that the uppermost limit of the working fineness has been or will shortly be reached even by such an improved method.
In recent years, on the other hand, demand is growing, among high-performance semiconductor devices, for application-specific ICs (ASICs) specifically designed to meet a particular application. Manufacture of ASICs unavoidably has a problem in respect of the production of a large number of different grades each in a relatively small quantity. This problem necessarily leads to a difficulty in preparing respective photomasks for the particular ASICs taking large costs and time to cause a serious delay of the product delivery and economical disadvantages.
In order to comply with the demand growth for ASICs by avoiding the above mentioned problems, it is a subject matter of intensive investigations in the electronics industry to directly effect patterning of a resist layer without using a photomask, for example, by a controlled scanning of electron beams on a resist layer formed from an electron beam-curable resist composition. This method of electron beam patterning is promising in respect of the highest fineness of patterning where a fineness of 0.5 .mu.m or finer can be obtained relatively easily on the surface of a silicon wafer. It is essential in the electron beam patterning of a resist layer that the electron beam is narrowed down to have a very small diameter not exceeding 0.5 .mu.m to obtain clear demarcation between adjacent patterned lines without overlapping. The electron beam-curable resist composition accordingly should meet several requirements that the contrast of the images obtained therewith is sufficiently high with a difference in the solubility as large as possible between the irradiated and unirradiated areas, that a line pattern obtained therefrom has a cross sectional profile as close as possible to complete orthogonality on the substrate surface, and so on.
It is a remarkable fact that a resist composition having excellent performance as a photoresist composition is not always excellent as an electron beam-curable resist composition. For example, the photosensitive resin composition useful for making a printing plate disclosed in U.S. Pat. No. 3,697,274, which comprises an amino resin, melamine resin and organic halogen compound, is not suitable as an electron beam-curable resist composition. Examples of electron beam-curable resist compositions hitherto developed include those comprising a poly(methyl methacrylate) resin disclosed in Japanese Patent Publication 45-30225, poly(glycidyl methacrylate) disclosed in Journal of Electrochemical Society, volume 118, page 669 (1971) and chloromethylated polystyrene disclosed in Japanese Patent Kokai 57-176034.
A problem in these electron beam-curable resist compositions in the prior art is that the developer used for the development treatment thereof is an organic solvent to cause environmental pollution and adverse influences on the workers' health even by setting aside their relatively poor performance as a resist material that scums are sometimes formed on the resist pattern after development and adjacent line patterns sometimes overlap on each other with poor resolution to affect the accuracy of the resist pattern, that the cross sectional profile of the line pattern obtained therefrom sometimes deviates from orthogonality and the contrast of the images obtained using them is sometimes too low.
On the other hand, a resist composition capable of being patterned by the irradiation with excimer lasers, far ultraviolet light and X-rays followed by development with an aqueous developer solution is disclosed in Japanese Patent Kokai 62-164045. The composition, which comprises a thermosetting resin and an organic halogen compound capable of absorbing chemical rays at a wavelength of 210 to 299 nm to act as a photolytic acid generator, is suggested to be sensitive also to electron beam irradiation. The fact is, however, that the patterned resist layer formed from such a composition by patternwise irradiation with electron beams has poor contrast of the images and the line pattern thus formed is far from orthogonality in the cross sectional profile sometimes having trailing skirts not to give high resolution of extremely fine patterns if not to mention the impractically poor storage stability of the resist composition in the form of a solution.